public class text_7 {
//1—2+3-4+5……+99-100
public static void main(String[] args) {
        double sum = 0;
        for (int i = 1; i <= 100; i++) {
            if(i%2==0){
                sum = sum-1.0/i;
            }else {
                sum = sum+1.0/i;
            }
        }
        System.out.println(sum);
    }
}
